Fix multi arch build with new buildx

What's Changed

• Fix single platform build on buildx >= 0.10 by @ddosia in #9

Full Changelog: v0.6.0...0.6.1

v0.6.0

What's Changed

• Use buildx by default; add multi platform build by @ddosia in #8

Full Changelog: v0.5.0...v0.6.0